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Message-ID: <20240502090553.485bf36b@device-28.home>
Date: Thu, 2 May 2024 09:05:53 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Heiner Kallweit <hkallweit1@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com, Andrew Lunn
<andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>, Eric Dumazet
<edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Russell King
<linux@...linux.org.uk>, linux-arm-kernel@...ts.infradead.org, Christophe
Leroy <christophe.leroy@...roup.eu>, Herve Codina
<herve.codina@...tlin.com>, Florian Fainelli <f.fainelli@...il.com>,
Vladimir Oltean <vladimir.oltean@....com>, Köry Maincent
<kory.maincent@...tlin.com>, Jesse Brandeburg <jesse.brandeburg@...el.com>,
Marek Behún <kabel@...nel.org>, Piergiorgio Beruto
<piergiorgio.beruto@...il.com>, Oleksij Rempel <o.rempel@...gutronix.de>,
Nicolò Veronese <nicveronese@...il.com>, Simon Horman
<horms@...nel.org>, mwojtas@...omium.org, Nathan Chancellor
<nathan@...nel.org>, Antoine Tenart <atenart@...nel.org>
Subject: Re: [PATCH net-next] net: phy: Don't conditionally compile the
phy_link_topology creation
Hi,
On Tue, 30 Apr 2024 23:29:37 +0200
Heiner Kallweit <hkallweit1@...il.com> wrote:
> On 30.04.2024 13:57, Maxime Chevallier wrote:
> > Hello Heiner,
> >
> > On Tue, 30 Apr 2024 10:17:31 +0200
> > Heiner Kallweit <hkallweit1@...il.com> wrote:
> >
> >> On 29.04.2024 15:10, Maxime Chevallier wrote:
> >>> The core of the phy_link_topology isn't directly tied to phylib, and at
> >>> the moment it's initialized, phylib might not be loaded yet. Move the
> >>> initialization of the topology to the phy_link_topology_core header,
> >>> which contains the bare minimum so that we can initialize it at netdev
> >>> creation.
> >>>
> >>
> >> The change fixes the issue for me, but according to my personal taste
> >> the code isn't intuitive and still error-prone. Also there's no good
> >> reason to inline a function like phy_link_topo_create() and make it
> >> publicly available. Do you expect it to be ever used outside net core?
> >> In general it may make sense to add a config symbol for the topology
> >> extension, there seem to be very few, specialized use cases for it.
> >
> > I think I'm missing the point here then. Do you mean adding a Kconfig
> > option to explicitely turn phy_link_topology on ? or build it as a
> > dedicated kernel module ?
> >
> > Or do you see something such as "if phylib is M or Y, then build the
> > topology stuff and make sure it's allocated when a netdev gets created
> > ?"
> >
> > Thanks,
> >
> > Maxime
> >
> >>
> >>> Signed-off-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
> >>> Closes: https://lore.kernel.org/netdev/2e11b89d-100f-49e7-9c9a-834cc0b82f97@gmail.com/
> >>> Closes: https://lore.kernel.org/netdev/20240409201553.GA4124869@dev-arch.thelio-3990X/
> >>> ---
> >>> drivers/net/phy/phy_link_topology.c | 23 --------------------
> >>> include/linux/phy_link_topology.h | 5 -----
> >>> include/linux/phy_link_topology_core.h | 30 +++++++++++++++++---------
> >>> 3 files changed, 20 insertions(+), 38 deletions(-)
> >>>
> >>> diff --git a/drivers/net/phy/phy_link_topology.c b/drivers/net/phy/phy_link_topology.c
> >>> index 985941c5c558..960aedd73308 100644
> >>> --- a/drivers/net/phy/phy_link_topology.c
> >>> +++ b/drivers/net/phy/phy_link_topology.c
> >>> @@ -12,29 +12,6 @@
> >>> #include <linux/rtnetlink.h>
> >>> #include <linux/xarray.h>
> >>>
> >>> -struct phy_link_topology *phy_link_topo_create(struct net_device *dev)
> >>> -{
> >>> - struct phy_link_topology *topo;
> >>> -
> >>> - topo = kzalloc(sizeof(*topo), GFP_KERNEL);
> >>> - if (!topo)
> >>> - return ERR_PTR(-ENOMEM);
> >>> -
> >>> - xa_init_flags(&topo->phys, XA_FLAGS_ALLOC1);
> >>> - topo->next_phy_index = 1;
> >>> -
> >>> - return topo;
> >>> -}
> >>> -
> >>> -void phy_link_topo_destroy(struct phy_link_topology *topo)
> >>> -{
> >>> - if (!topo)
> >>> - return;
> >>> -
> >>> - xa_destroy(&topo->phys);
> >>> - kfree(topo);
> >>> -}
> >>> -
> >>> int phy_link_topo_add_phy(struct phy_link_topology *topo,
> >>> struct phy_device *phy,
> >>> enum phy_upstream upt, void *upstream)
> >>> diff --git a/include/linux/phy_link_topology.h b/include/linux/phy_link_topology.h
> >>> index 6b79feb607e7..ad72d7881257 100644
> >>> --- a/include/linux/phy_link_topology.h
> >>> +++ b/include/linux/phy_link_topology.h
> >>> @@ -32,11 +32,6 @@ struct phy_device_node {
> >>> struct phy_device *phy;
> >>> };
> >>>
> >>> -struct phy_link_topology {
> >>> - struct xarray phys;
> >>> - u32 next_phy_index;
> >>> -};
> >>> -
> >>> static inline struct phy_device *
> >>> phy_link_topo_get_phy(struct phy_link_topology *topo, u32 phyindex)
> >>> {
> >>> diff --git a/include/linux/phy_link_topology_core.h b/include/linux/phy_link_topology_core.h
> >>> index 0a6479055745..0116ec49cd1b 100644
> >>> --- a/include/linux/phy_link_topology_core.h
> >>> +++ b/include/linux/phy_link_topology_core.h
> >>> @@ -2,24 +2,34 @@
> >>> #ifndef __PHY_LINK_TOPOLOGY_CORE_H
> >>> #define __PHY_LINK_TOPOLOGY_CORE_H
> >>>
> >>> -struct phy_link_topology;
> >>> +#include <linux/xarray.h>
> >>>
> >>> -#if IS_REACHABLE(CONFIG_PHYLIB)
> >>> -
> >>> -struct phy_link_topology *phy_link_topo_create(struct net_device *dev);
> >>> -void phy_link_topo_destroy(struct phy_link_topology *topo);
> >>> -
> >>> -#else
> >>> +struct phy_link_topology {
> >>> + struct xarray phys;
> >>> + u32 next_phy_index;
> >>> +};
> >>>
> >>> static inline struct phy_link_topology *phy_link_topo_create(struct net_device *dev)
> >>> {
> >>> - return NULL;
> >>> + struct phy_link_topology *topo;
> >>> +
> >>> + topo = kzalloc(sizeof(*topo), GFP_KERNEL);
> >>> + if (!topo)
> >>> + return ERR_PTR(-ENOMEM);
> >>> +
> >>> + xa_init_flags(&topo->phys, XA_FLAGS_ALLOC1);
> >>> + topo->next_phy_index = 1;
> >>> +
> >>> + return topo;
> >>> }
> >>>
> >>> static inline void phy_link_topo_destroy(struct phy_link_topology *topo)
> >>> {
> >>> -}
> >>> + if (!topo)
> >>> + return;
> >>>
> >>> -#endif
> >>> + xa_destroy(&topo->phys);
> >>> + kfree(topo);
> >>> +}
> >>>
> >>> #endif /* __PHY_LINK_TOPOLOGY_CORE_H */
> >>
> >
>
> To go a little bit more into detail:
>
> phy_link_topo_create() and phy_link_topo_destroy() are used in net/core/dev.c
> only. Do you expect them to be ever used by other callers?
> If not, their functionality could be moved to net/core/dev.c.
> Supposedly guarded by IS_ENABLED(CONFIG_PHYLIB), alternatively a new config
> symbol for link_topo support.
>
> To get rid of the dependency you could also lazy-inizialize
> netdev->link_topo. For this phy_link_topo_add_phy() would have
> to take the netdev as first argument, not the topo.
> Then the first call to phy_link_topo_add_phy() would initialize
> netdev->link_topo.
>
> I think functions like phy_link_topo_get_phy() should also check for
> topo != NULL first, maybe combined with a WARN_ON().
> They are exported and you have no control over its use.
Thanks Heiner for the explanations. I'll rework based on that. The
original reason I didn't directly include the netdev as a parameter for
these function, or didn't put any helper in net/core/dev.c is because I
wanted to avoid too strong of a link between the topology and netdev.
There are some PHYs for which we can't assign any netdev (PHYs that
would sit in-between 2 chained DSA switches is the only example I have
in mind though), but TBH the code in its actual shape doesn't address
these either, so it's a useless design constraint.
So, let me indeed do that, it will probably make for a simpler and more
straightforward design.
Thanks for the input,
Maxime
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